The number of vehicles such as automobiles mounted with an onboard camera for picking up images of surrounding circumstances around the vehicles has been increasing. The images picked up by the onboard camera are very convenient because they can be used for support of steering for parking, judgment of a possibility of a crash between the vehicle and an object, and so on.
In the case of using the images picked up by the onboard camera, it is important to accurately calibrate the mounting angle of the onboard camera relative to a road surface. Onboard camera calibration methods of this kind include a method using an already-known object (calibration target) arranged at a predetermined position on a road surface in advance.
In the case of calibrating the mounting angle of the onboard camera relative to a road surface using the calibration target installed on the road surface in advance, however, the state of the vehicle at the time of calibration being performed does not necessarily correspond to the actual state of the vehicle at the time of the vehicle running. For example, the mounting angle of the onboard camera relative to the road surface changes depending on the number of passengers or fluctuation in the load. Therefore, the calibration using a calibration target is insufficient as calibration for the mounting angle at the time of the vehicle is running. The mounting angle of the onboard camera relative to the road surface also changes due to change over the years after the calibration using a calibration target.